Method of operating alternating-current motors.



R. D. MERSHON.

METHOD OF DPERATING ALTERNATING CURRENT MOTORS.

APPLICATION FILED JAN. 25, 1904.

913,415. Patented Feb. 23, 1909.

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R. D. MERSHON.

METHOD OF OPERATING ALTBRNATING CURRENT MOTORS.

APPLICATION FILED JAN.25,1904.

Patented Feb. 23, 1909,

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R. D. MERSHON. METHOD OF OPERATING ALTERNATING CURRENT MOTORS.

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R. D. MERSHON. METHOD OF OYERATING ALTERNATING CURRENT MOTORS.

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R. D. MERSHON. METHOD OF OPERATING ALTERNATING CURRENT MOTORS.

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RALPH D. MERSHON, OF NEW YORK, N, Y.

METHOD OF OPERATING ALTERNATING-OUBBENT MOTORS.

Specification of Letters Patent.

Patented Feb. 23, 1909.

Application filed January 25, 1904. Serial No. 190,440.

To all whom it may concern:

Be it known that I, RALPH D. M ERSIION, a citizen of the United States, residing at New York, in the county and State of New York, have invented a certain new and useful Method of Operatin Alternating-(Jurrent Motors, of which the ollowing is a s ecification, reference being had to the rawings accompanying and forming part of the same.

My lnventlon relates to the operation of alternating current motors, more particularly for the purpose of varying the speed thereof. I

As is well known, the chief obstacle, if not practically the only obstacle, to the use of alternating current motors where direct current machines are now em loyed is the fact that at present known to the art there is no method of varying the speed of an alternatmg current motor which does not possess senous defects. In operating railways, elevators, and other apparatus, in which considerable variation 0' speed is necessary ordesnable, the direct current motor is now almost universally used, although in many other res cts the alternating current motor 1s prefera le. A number of ways have been proposed and to some extent used, for obtaming the capability of speed variation so much desired. One method is to use a rheostat in the secondary, in the well known manner. This secures the desired result, but with such a loss in the elliciency of the alternatmg current motor as to render the plan objectionable. Another method, known as concatenated control, is sometimes used where two or more motors are connected to the sameload, but in this case a rheostat must be employed with at least one of the motors, besides other objections inherent to the "eoncatenated connection. Still another method is to vary the number of poles in the energizing circuits, with correspondin change of speed, but, as heretofore practiced; the loss in efficiency by this method may be so great as to be rohibitive. Recourse must therefore genera ly be had to direct current machines, although, as before stated, the alternatmg current motor is in many other respects superior.

In some cases the necessity of using direct current motors becomes particularly objectionable, as when power is to betransmitted over long distances, over a system of distribution many miles in extent, or from a distant water power or other source. Under such conditlons it is necessary to generate alternating current, transmit it at high tension to the point of utilization, and then, by means of costly apparatus and attendance, convert it into direct current. The power must be transmitted by alternating current, since with direct current the loss in transmission would be enormous unless the conductors were impractically large or expensive. l-Iav' 'by means of the efficient and economical a ternating apparatus delivered the power to the point where it is to be utilized, the current must then be rectified, with a resulting loss of a large proportion of the previous saving, merely because alternat' current motors do not possess that practic capability of speed control which is so indispensable.

To avoid the necessity, and consequent expense, of rectifying the current, a system has been proposed particularly for use in connection with ra' ways, in which the alternating current from the line energize a motor on the locomotive or car, which in turn drives a direct current generator, also on the car. Current from the latter generator is then supplied to a second direct current motor, also on the car, which in turn propels the vehicle. This plan has advantages for certain purposes, but, at best, it always requires three machines to do the work of one, on each propelling vehicle. By operating a motor accordingbto my invention, however, the speed may varied as readily as in a direct current machine, of the latter, such as large rheostatie losses and the disadvantages of a commutator, and at the same time my method W be found to possess none of the objectionabii features found in the previous methods of varying the speed of an alternating current motor. The invention also ppss numerous positive advantages. the first place since it enables a motor to be employed whieh'is 0 rated by alternat currents, the use oi i'otary converters an their maintenance are dispensed with, and the economy of alternating current generation is therefore preserved. In long distance transmission the only intermediate apparatus required a the transformer or transformers ry to step-down the voltage to the rope! int. Again, no rheostat is necessari y use and there need therefore be no rheostatic loss without the defects fouihpcles and wit when the motor is runmng' at less than normal or full load speed. For example, in bringing the motor and its load from rest to maximum speed, or in running at any speed less than maximum, there would be no loss of power in a rheostat, and the motor, at an intermediate speed as well as at maximum, consumes approximately only so much power as is required to carry the load at that particular speed. A further advantage, and one of the most important, is the econom efiected in stopping the load, or bringing it from a her to a lower speed. In such cases the Inertia of the moving masses, or, stated otherwise, the kinetic energy stored in the load, instead of being wasted in the brakes, is transformed int c ectrical ener by the motor and is delivered to the supp y circuit to be utilized by other motors or translating devices connected therewith. This feature of the invention is of special value in traction systems, where eavy trains with enormous inertia,'have to be brought from high s eed to a stop. The otential energy of the load is also transormed into electrical ener and delivered to the line, as for exam Is in the caseiof a train running down gra e. Here, as before, instead of applyi the brakes to keep down or reduce the s cc the motor itself receives the energy an returns it to the supply circuit. Another instance which may be mentioned in this connection is a descending elevator car. Here the potential energy, which is not inconside'rable', may be returned to the supply circuit and utilized to aid in raising ot or cars. In fact, it may be said, generally, that the motor will consume approximately only enough ower to carry the load at the desired spee whatever that may be, and that when from any cause the load itself is developing powerthe same may be transformed into useful energy and returned to the supply circuit, instead of being wasted as is now commonly the case.

The invention itself which is based on th phrinciple of varying the number of oles in e motor will be more readily un erstoodwhen exp ained in connection with the accompanying drawings, in which- F re 1 1s a diagram in which the curves therein shown re resent the performance of a single phase in uction. motor with various numbers of poles, operating both as a motor and as a generator. Fig. 2 is a diagram showing a typical system arranged for the practice of my invention, in the case of a single phase induction motor. Fig.3 shows diagrammatically a system aned for practicing my invention in the case 0 a twohase motor. In the arrangement shown, motoris adapted to be operated with two poles. 4 shows ano er arrangement of connections to give is plotted the speed of the motor in those of maximum torque,

negative respectively; while t e hnes 0-ffeur poles. Fig. 5 shows the connections for two poles. Fig. 6 illustrates another arrangement for two poles in a two-phase motor. Fig. 7 is a diagram illustrating a novel method of effecting a cha e from one number of poles to another. ig. 8 is a dia ram showing a twoole induction motor an the flux distribution therein. Fig. 9 shows flux waves in the secondary for various widths of circuit. Fig. 10 is a diagram showing a two-pole induction motor with two leads er pole, and the resulting flux distribution. Fi 11 shows flux waves in the secondary of t motor for various widths of circuit. Fig.12 shows the ordinary method of constructing the secondary, and Fig. 13 shows a novel construction for securing any desired width of circuit in the secondary. Fig. 14 shows a twoole single phase motor, with the current Is in at three oints er pole, and shows also the form 0? the ux wave resulting from such connection. Fig. 15 illustrates a system, with a single hase motor, for practicing my invention in c anging the number of poles and securing a desired flux distribution.

The apparatus shown-in the drawings have Gramme ring windings only, but it will, of course be obvious that this type is merely illustrative, and that the invention is applicable to any other suitable winding, as for example drum windings.

R erring nowtto Fig. 1, in which is represented by means of curves the performance of a single phase induction motor with various numbers of poles, on the vertical axis ercentage of the synchronous speed w ch corresponds to the least number of else at which the motor is to operate. On t e horizontal axis, to the right, is plotted the positive torque of the motor in coming to a higher speed, and to the left, the negative torque in coming to a lower speed; both in percentage of the maximum positive torque which the motor can exert. The value at which the line a b cuts the vertical axis is that of synchronous speed for the least number of poles; the values at which the lines cd and cd cut the horizontal axis are ositive and and e.j indicate respectively a positive and a negative torque ess than maximum which ma be called the rated or normal tor us. see curves as previouslystated, are hose for a s' le p e induction motor, but the correspon curves for apol hase motor are similar, the main difierence eing that the polyphase curve instead of passing through zero cuts the horizontal axis at'a torque value depending upon the design of the motor. In all other respects, however,

the two c of curves are very similar,

and the following explanation for the single phase applies equally well mane polyphase having except that in the latter case auxilia starting means would not necessarily e employed. Disregardmg for the present the dotted curves, the curve A represents the performance of a motor when running with its least number of poles. It will be ob served that in this case the speed rises more rapidly than the torque up to a certain point, after which the torque increases rapidly to a maximum at a speed slightly lower than synchronous. The discrepancy between the curve of actual erformance and the straight line g-h, whic represents what would be the performance of the system if the speed and the torque rose together until maximum torque were reached, 18 wide. Since it is a fact that with a greater number of poles maximum torque will be reached at a speed proportionately lower than the synchronous s eed of the first case, other curves may be p otted by which the actual performance of the motor with various numbers of poles may be compared.

.n Fig. 1 the curve A may be understood to be the curve resulting with 8 poles. Increasing the number to 10, or 10/8 of the former number, the curve B results, the

curves (3 and D showing the performance with successive increases in the number of poles. In the case of curve B, the synchronous speed is 80 per cent. of the first; in curve 0 there are l2/8-the first number of oles, and the synchronous 3 ed is there'- ore 66 2/3 per cent. in curve 14/8 the first number of poles are used, and the synchronous speed is therefore 57 1/7 per cent.; and so on or as rest a number of poles as desired. It will now be seen that with such a motor as this, if the torque re uired of it were no ater than that where t e line e-f cuts the orizontal axis, the motor could be started, that is, brought-to its normal speed, or the speed corresponding to its least number of Ice, by bringing it, as by means of any auxi my device, either mechanical or electrical, to the comparatively low speed corresponding to its; greatest number of poles, or approximately to that speed; the number of poles is'tlien decreased to such a number that, with the speed previously existing the torqlpe with the new number of poles will not fall elow the predetermined torque, such as for example that indicated by the line. e-f. Stated otherwise, the reduction in the number of poles must be such that the int of intersection of the curves D and C alls beyond the line 0-;1'. The reduction can effected, the motor, and the load to which it may be connected is allowed to increase in' speed toward s chronism for the new number of poles. Vli l ien its speed has increased sufiiciently the number of poles may he again reduced, in subst ntially the same manne as before. After the step the =peed of the motor and load will again in- .by a series of steps.

crease; and by repeating such steps as often as necessary the motor and load may finally be brought to the speed corresponding to what may he termed its normal number of poles. In other words, the single phase motor when operated according to my method becomes, from a comparatively low speed, a self-starting and variable speed motor by a simple commutation of its poles. This commutation can be performed by a process of manipulation comparable to that of a starting rheostat or other controlling mechanism. At any intermediate speed, moreover, this motor would operate as a constant speed motor for that particular number of poles. That is, under any load which it is capable of carrying, it runs at approximately constant s eed; whereas the s eed of a motor control ed by a rheostat fal s off as the load is increased, unless the rheostat be manipulated. It should be further noted that whereas in the case of an ordinary single phase motor, for example one represented y curve A, stat-ted by electrical auxiliary means, a power com onent proportional to the maximum sync ironous s eed of the motor'must be supplied by t e auxiliary starting device, in t ie present case the component required is pro ortional only to the synchronous speed of t :e reatest number of poles. For instance, if t ie motor have an output of 100 II. P. at the least number of poles, and it be started with this number of poles, it will require at starting an auxiliary com onent of power proportional to 100 H. 1 but if its greatest numberof poles be ten times that of the least number, it will require when starting with the greatest number an auxiliar component, proportional to only 10 H.

Obviously an suitable device for supplying the out of p ase component may be employed, such as re-actance coils, or condensers, or both, for connection to suitable ints of. the motor windings, orfor derivmg, externally to the motor,'an out of phase component which will then be sup lied to the motor, or an induction or sync ronous polyphase motor receiving power in one phase from the main source and delivering the out of ass component from one or more other circuits of its winding.

As will be seen from Fig. 1,. the s eed rises It is obvious t at these steps. may be made less abrupt by using a larger number of poles for the maximum speed and a dproportionall larger number in starting, an increasing t in the complete reduction, so that the curves will more nearly merge. The solid line curves of Fig. l are those resulting when the voltage has throughout the entire operation, for each number of pole s,-:-f-.'the value which may be considered normal for that number of poles. list any time, as for instance at the time of making the change from one number of poles to another, the voltage be made greater than the normal value, the torque which the motor can exert will in consequence be increased. The erformance of the motor with varying numbers of poles and simultaneous abnormal increase in the voltage, is represented by the dotted curves in Fig. 1. Here it will be noted that the dot-. ted curve B cuts the curve C at a highertorque than does the curve B. This makes it possible to operate the motor with a higher torque than before, and as an example of this method, su pose the motor to be running on 0; let t e motor run up to the desired speed, as to the (point a, then reduce the number-of oles an increase the Volta e, whereupon t e motor will take the curve after running on that curve until the desired speed is attained, say at the point b, the voltage may be reduced to normal with consequent drop in torque (but no fall in speed) to a point I) on the curve B running on this curve until the speed has increased the desired amount, as at the point b the number of poles is again decreased, and the voltage abnormally increased, whereupon the motor takes curve A; after rising in s eed as desired, for instance, to the spee at a, the voltage may be reduced again to normal; the torque then drops to the point a on curve A. By this method the torque which the motor exerts through the operation may be made to approach the maximum torque at normal voltage as nearly as desired; or by proper variations in the voltage the tor us at the instant of change of poles and t oughout the consequent change of s eed can be raised to ractically any desire value. The same met od may be employed to avoid the necessity of using a large number of steps in changing the number of poles. For example, starting on the curve D, suppose when the speed has reached the proper point, say at d the number of poles be re duced, not to the number corresponding to the curve C, but to a number somewhere between B and C. At the same time? increase the voltage. The curve then resulting will cut the curve -D at or beyond the line ell-Hf, and the motor will, if the voltage be s ciently abnormal, therefore increase in speed toward that correspond to synchronism for thenew number of po es; whereas if the voltage had not been increased the" torque where the two curves will intersect would have been, or might have been, .below that neeess to c the load, as for example, that indicated by the line e-f. When the motor on the new. curve has reached the .qpsired speed, by reducing the number ofpo es to that corresponding to curve A, and simultaneousl increasing the voltage, the motor may be brought to the speed of a", as before. u the latter case, however, it will be noted that only two ch es in the num-'- ber of poles were required to ring the motor up to its normal or maximum speed, without fall below the predetermined torque, while in t e former instance three ch es in the number of poles were required to ring the motor to the same ultimate speed.

It will be seen that there is a relation between the magnitude of the steps. in changing the number of poles, the voltage impressed at the instant the change is made, and the torque of the load which the motor can brin up from its lowest to its highest speed. I the voltage impressed on the motor never be increased be ,ond that which may be considered normal or each number of poles, then the smaller the steps by which the number of poles is varied, the more nearly will the maximum load torque, which the motor cari maintain asit increases in speed, approach the maximum torque that t e motor can exert with any 'ven number of poles at normal voltage. 1', with any given ma nitude of step in changin the number oi poles, the load torque whici the motor can maintain throughout its range of s eed may be made to approximate as c osely as desired the maximum torque that the motor can exert with any 'ven number of poles at normal voltage, by increasing, at the instant the chan e in the number of poles is made, the v0 tage toa value sufliciently above that which may be considered normal for the new number of poles. It will therefore be seen that by properly proportioning the ma 'tude of the pole changes, and the va us of the voltage im-V pressed at the time the chan e in the number of poles is made, it is possi le to maintain, during the change from a speed corresponding to one number of polestothat corresponding to another, a torque equal to, or ter than, a predetermined torque whic predetermined torque is less than the maximum that the motor can exert with any 'ven number of poles at normal volt e. reducing the voltage to normal a er an abnprrlillal value has been d Wm mu 0 t e urposes mentione it e y be fouIi d advisable, if the abnormafir i crease were considerable, to make the reduction by two or more steps, in order not to make the dro in torque too sudden.

e operations described throughout the foregoing are applicable equal]. well for the pn ose of re uc' theslpeed of a motor an its load, either m in ornormal speed to rest, or from any higher speed to a lower.

' This method is also illustrated in Fig. 1, but,

on the left side of the vertical axis. Here solid curve K represents the performance of the motor when drivenl/bg the inertia or potential one of the oa as a generator with its norms. or least number, of poles. The torque of the motor is now-negative, and

employed for either will oppose the load and reduce its speed. Suppose for example, the motor to be running with a speed and negative torque corresponding to the oint k on the curve K; then the speed wi diminish; and when it has fallen to, say a point k, the number of poles is increased to that corresponding to the curve H, but at the same time there is impressed a voltage sufficiently above normal to bring the motor to another curve, such as H. The motor is then allowed to drop in speed along H until it reaches a suitable point, as h, at which instant the voltage is changed to the value normal for the number of poles corresponding to curve 11, thus bringing the motor to the oint h. This process me. be continued till t e motor has been broug t to rest or to the desired lower speed; or in the case where the motor has potential enel which it is desired to deliver to the line w rile maintaining the load at constant speed, as in the case of a train going down grade, the motor may be allowed to operate at any desired number of oles, :4 thus maintaining the load at the speed cor- 'esponding to such number of poles, and continually delivering its potential energy to the line. By increasing the voltage s1- multaneously with the change or cha es in the number of poles results are secure corresponding to those in the case described above for increasing the speed. That is, a higher negative torque is utilized, with consequently greater retarding force, or a fewer number of steps employed in increasing the number of poles from the smallest to the greatest number.

Referring now to Fig. 2, I show here in diagram a system arranged for practicing my invention, in which G is a source of single phase current, M a motor having a stationary element 0, of any suitable type, as for example the (iramme ring shown, and a rotating induction element P. T indicates terminals connected to leads extending to the motor. It will here be seen, that as shown, the motor may be operated with four poles, and that for each e there are three eads. By using a plura ity of leads for each pole, as herein described, it is possible to secure in the primary winding any desired magnetic flux distribution. his feature I do notclaim broadly in this a plication, but do so in my copending app ication, Serial No. 174,698. T e connections of the auxiliary starting device, S, for the sake of simplicity, are shown as only one lead per pole for both main and auxilia motor. The current supplied to the main motor directl from the transformer Q is delivered throng three leads per pole; while in the case of the auxiliary motor S both the current thereto and the current therefrom to the main motor, are supplied throng? only one 65 lead per pole. If, however, an e ciency for the current delivered to the main motor throu h the agenc of the auxiliary S, comparab e to that 0 tained with the current supplied through the transformer Q is desired, the auxiliary motor should, for suplying its out-of-phase component, have lioth from the source G and to the main motor the same number of leads per pole as there are per pole from the transformer to the main motor. Ordinarily the auxiliary is in use such a short time that the additionll leads can in many cases be dispensed with, and I have therefore omitted them in the diagram to avoid unnecessarily complicating the fi e. The auxiliary starting device here i] ustrated is selected merely as a type, and is represented as a two hase motor, either synchronous or induction, recei current in one phase of its winding an delivering current from the other phase. In order to supply the three leads for each ole in the main motor, a transformer Q is introduced, having secondaries s s 8, connected b leads t t t t t t t' t" t, to the controller iagrammaticall indicated at C. This latter is so designs as will be seen by tracing out the connections, that in one position the motor will run with four poles; in the last position the connections will be for two poles.

Referring again to Fi 1, it will be seen that the speed varies or c anges in either direction, by a series of steps. It is obvious that these steps may be made less abrupt by usin a large number of poles for the highest s cc and increasing the number of ste in t e complete change from or to this number, so that the curves will more near y merge. Beyond certain limits, however, this increase in the number of poles to increase the number of increments becomes impracticable. I have therefore devised a novel method of interpolating one or more speeds in each step, thus approxlmatlng t e same result as with an infracticably large number of poles. The i ea w1llbe more readily understood from a concrete m stance, and for this purpose let it be supposed that the motor has connections for a maxb mum of four'poles, but is intended to run normally with two. In this case the reduction would be from 4 to 2. Instead, however, of making the change all around the motor, I chan only a part thereof, as for example one-ha to the two-pole connection so that it is on one side connected for twopole running, while on the other it is still connected for the four-pole. The motor therefore run at a compromise speed tween four and two poles. As soon as this s sad is reached, or approximately reached, the four-pole side is changed to the two- 10 connection, so that the entire motor is en connected for two poles. This method of rpduction is illustrateddiagrammatically m 130 7, in which N represents the motor with four-pole connections; Nfl the same with one side 0 d to two- Ye connections; and N" with other si e reduced to the twopole connection. It is lain of course that the method is not limite in every case to one interpolation, since the fractional parts of the motor on which the chan are made, need not be halves but may e thirds, or quarters, or such other fractional parts as desired if the number of poles will permit, thereby introduc' two, three, or more speeds. It is also 0 ear that this method is not confined to the case of a single base induction motor, but ma be ap lie to an motor in which the num er of es is varie either by increasing or decreasing their number. A further advantage resulting from this method of changing the number of les by making the change upon parts 0 the motor successively (or in any other suitable order), is the fact that there will be less tendency to destructive arcing, for the reason that at mtalillt ocfhdisco' nngcting the circuitsin te angeste wercarried by the circuits disconnected i shifted, at the instant of break to the circuits rem connected. The controller illus trated at O, 2, is adapted for making an inte lation In the first position of the contro er the motor is connected for four poles; in the next position one side of the motor is connected for two poles, while the other side remains as before with four-pole connections; and finally in the last position, the; motor is connected on both sides for two ea Referring now to Fig. 3, this figure shows a system arranged for the application of my method in the case of a lyphase motor, as for exam le one operated by two phases as shown. he quarter phase source is indicated by A B, between which'and the motor are transformers Q, Q. As will be seen by tracing out the connections,-the motor has a maximum number of poles, four, and a minimum number, two, thereby gi two speeds. Each pole is supplied by two ends, instead of one as is ordinarily the case. The additional lead per pole is provided for the glip'pose of secu a desired magnetic flux tlibution, as be ex lained more fully hereinafter. The system illustrated in Fig. 3 also provides for supplying an abnormal voltage along with the c ange in the number of po es. For example, when starting the motor with the higher number of poles, with the switches R to the right, there is first impremed upon the motor a higher voltage, that is, higher than that which may be considered normalfor that number of poles. The result ,curve of performance is analogous to the em taken by those in Fig. 1, with the important difierence that the motor being self-starting from rest, the curve will,

as previously explained, not begin at the origin, but somew ere out on the horizontal axis instead. The next change gives a lower voltage, which may be considered normal for that number of poles. In passing from the higher number-to the lower number of poles a similar change of volta e takes place, that is, there is first im resser? mal voltage, and t en the normal. In coming from the lower number of oles to the higher, in reducing the speed 0 the motor, the switches R are thrown to the left, which results in a higher volt e at the instant the change in the number 0 poles is made.

The system shown in Fig. 4 is one which in some cases might be used instead of that shown in Fig. 3. It gives four poles with ei ht leads instead of sixteen, but the electrical chord between leads is twice as great. Fig. 5 shows the corresponding two-pole connection this system. No controller is shown in either. of these diagrams, as they are 'ven simply to illustrate one of the ways in w 'ch the number of leads may be reduced in cases where the electrical chord between leads may be increased or where a lead may be made common to two phases. Or, the twoole connection might be as in Fig. 6, but ere the electrical chord is one-half that of the"system shown in 5.

In 4, 5 and 6, A-B indicate the source 0 uarter-phase current, and P indicates the primary of the machine. Q1, Q" indicate auto-transformers from which t e plurality of leads per pole are supplied with current.

. For reasons well known to those skilled in the art, it is ordinarily desirable that the E. M. F.s induced in the circuits of a motor shall closely approximate a sim le 'sine wave. This will be accomplished if t e flux waves in these circuits closely a proximate a simple sine. With a given ux distribution in the motor the flux wave in these circuits may for a given number of poles be made to be or to closely approximate a simple sine by properly choosing the width of the electric are or chord embraced by these circuits; but if the desired end is attained in this way, any change in the number of poles, the flux distribution remaining the same, will result in a deviation from the approximation previousl obtained, the degree of deviation depen ing upon the ratio of the new number of poles to the former number, being in general greater the more this ratio departs from unity. If the flux distribution in the motor were a simple sine or a close approximation thereto, the flux wave in the secondary circuits, no matter what their width, and no matter what the number of poles, would be a simple sine er a close approximation. We may, therefore, maintain such a flux wave in the circuits, whatever their width, b ways maintaining in the motor a flux tria higher or abnorbution which is a simple sine or a close ap- I producing them, or, what is equivalent, by

proximation thereto; or we may maintain a close approximation to a sine wave under the conditions first mentioned (in which, with a distribution which is not a close approximation, an approximation to a simple sine flux wave is 0 tained by properly proportioning the width of the circuits), if on changing the numbers of poles we also change the flux distribution to a closer ap roximation to a simle sine. In other words, if for any reason it is desirable not to maintain a simple sine flux distribution, or an approximatlon thereto, under all conditions, an ap roximation to a simple sine flux wave may e maintained in the circuits by properly proportioning the width of the c1rcuits for one number of poles and for the flux distribution which does not closely approximate a simple sine, and, when a change in the number of poles would cause the flux wave to depart from a simple sine to an objectionable extent, improving at the instant the number of poles is changed the flux distribution to a degree which will maintain the wave at the approximation desired.

In illustration of how a desired flux distribution may be obtained I will explain the method in connection with a single phase induction motor, though the method is applicable as well to polyphase induction motors, and to synchronous motors both single and polyphaser Referring now to Fig. 8, this shows at U a single phase, uniformly wound motor of two poles having its currents supplied at opposite ends of a diameter. The resulting flux wave in the motor is that shown at u, the values on the horizontal axis being distances around the circumference of the motor U, the'length d-d' corresponding to 180 degrees of the motor circumference. The quantities plotted on the vertical axis represent the magnetic flux intensity in the motor corresponding to the various points in its circumference plotted on the horizontal axis. In Fig. 10, V represents the same motor but with the currents led in at four points, p, p, p, p. The resulting flux distribution curve is 1:, which, as will be seen, is closer to a simple sine wave than is 11., Fig. 8. The length of the fiat portion of the curve 1), indicated by a, depends u on the distance lead 12 is from ead p, and ead p from lead p, and may be increased or diminished as desired, by correspondingly va g these distances. Fig. 1 4 shows at W imame motor, but with the current led in at six points. Solid curve 'w shows the flux distribution (which, as will be seen, is astill closer approximation to a simple sine than is 'v), produced as the resultant of the components shown in dotted hnes. It will be noticed that the two components are similar to curves u and u of Figs. 8 and 10 respectively. The relative.

magnitudes of the components may be varied by varying the relative values of the currents varying the relative values of the voltages impressed on the circuits through which the currents producing the components flow. It will be seen, therefore, that b varying the length of the flat portion of t e component corresponding to 'u, and the relative magnitudes of the two components, we may obtain a close approximation to a simple sine wave. This method might be carried still further and currents led in at 8 or 10 points, or more, each increase in the number of currents led in enabling a still closer approximation. The method, which is of course applicable whatever the number of poles may be, or whatever the distribution may be which it is desired to approximate, or whether the winding be uniformly or non-uniformly distributed, is explained more in detail in my co-pending application, Serial Number 174,698, and claimed broadly therein, as before stated. Continuing, it may be said, in general, that the greater the number of leads per ole the more nearly can the flux distribution made to approximate any desired distribution. For example, when approximating a sine flux distribution, the degree of approximation can ordinarily be made close enough with five leads per pole; and indeed even with less leads per pole than this, as for instance two per pole or even at times with one. when for any reason the motor will not be operated for any great len th of time at a given number of poles, so t at its efficiency or the current taken by it at this number is not very important, a less favorable approximation to a sine distribution may not be seriously disadvantageous and consequently a small number of leads per pole may be employed. Such would often be the case with the verv lowest speeds at which the motor is operated. This is an advantage, since with the comparatively large number of poles for these lower speeds any reduction in the number of leads per pole very materially reduces the total number of leads to the machine. So in operating a motor where the efficiency, and therefore the distribution, at the lower speeds is not so important it may often be found advisable to operate inefficiently, and with a fewer number of leads per pole, at the lower speeds, and increase the number per pole as the hi her speeds are attained. I have, however, devised a plan b which, if desired, this course can be followed without serious sacrifice in efficieney at the lower speeds. This is the plan previously outlined, and consists in so-proportioning the electrical are or chord embraced by the secondary circuits of the motor that the flux wave in these circuits is a close approximation to that desired, even with the comparatively poor distribution Oi)- tained in th'e motor when the number of leads per pole is small, and as the number of poles is decreased and a greater number of leads per pole thus made available, improving the flux distribution by utilizing such leads and thus maintaining a good flux wave. This feature will be more fully described hereafter. Referring again to Fig. 8, U represents, as before stated, the winding of a two-pole motor with one lead per pole, the leads being 180 degrees a art. The resulting flux distribution in t e motor willbe as indicated by the curve a, in which electrical degrees are plotted on the horizontal axis, from d to d being 180 degrees, and flux intensity on the vertical axis. The curves at, -'u., a, Fig. 9, represent the flux waves generated by the fiux distribution of curve u, in secondary coils whose widths are such that they embrace 180, 90 and 60 degrees respectively. The points on the horizontal axis of these curves represent the positions of the middle points of their respective coils. These positions correspond to those, on the horizontal axis of the curve 11., at which the flux intensity values represented by the ordinates of u are measured The vertical ordinates of wa n, and u represent not flux intensit as in u, but the total flux throu h the co' s corresponding to the positions 0 their centers. In other words) if in the ma etic field of the motor U, the flux distribution of which is represented by the curve a, we rotate an electric circuit whose width is 180 degrees, the flux wave in this circuit will be the curve a. If the width of the circuit is 90 degrees the flux wave in it will be u, and if 60 degrees, the curve 11,. The dotted curve, 11., is a simple sine wave, assuming that this is the 'wave which it is desired to approximate. It will be noted that the curve u, for the 180 degrees circuit, and a, for the 90 degree circuit, fall on opposite sides of the sine wave it. somewhere between 180 degrees and 90 degrees there is some width of circuit which will have in it a flux wave which is exactly, or which very closely approximates, a simle sine wave. This curve may be found by trial or calculation, but of course its determination is not necessary here. So far we have spoken of the motor U, which has two poles, and in which therefore, electrical degrees and degrees of are are identical. The explanation already given in regard to the flux distribution wave, and the flux wave, will apply eqgieally well to a motor with a greater num r of poles, providing it be borne in mind in this case that the arcs mentioned are all electrical. In other words, if we should feed currents into the motor at four points instead of two, the flux distribution u would still be obtained, but the distance dd' instead of being 180 degrees of arc, would be 180 electrica degrees, which inthe case of the four poles corre sponds to 90 degrees of are. It should also be borne in mind that if with the four-pole .width of circuit between 180 an 10 and 11,

This shows that.

' etween 90 degrees and 60 degrees and connection we have a secondary circuit em= bracing 180 electrical degrees, and thus having in it a flux Wave corresponding to a, and that if we change from four poles to two poles, the same secondary circuit, which efore embraced 180 electrical degrees, will then embrace onl 90 electrical degrees, and will have in it t e flux wave 11.". Also, if for the four pole connection we em loy that 90 electrical degrees which will give the close approximation to a simple sine flux wave as previously described,-then on changing the number of poles to two the flux wave in this secondary will depart more from the simple sine wave than does it, because the secondary now embraces less than 90 electrical degrees.

An explanation similar to that already given for Figs. 8 and 9 will apply to ut' the latter represent con tions when two currents per ole are fed to the motor instead of one, as or example in the motor V, so spaced that the resulting flux distribution is that shown by curve 12. The corresponding flux waves for the distribution curve 1), in secondary circuits, embracing 90, 60 and 30 electrical degrees, are exemp ified by curves 1:, '0", 1:, respectively. Here, as before, the dotted curve, a, represents the simple sine wave which it is desired to approximate. In the case of v the difference between the two is so small that they are practically coincident. It will be seen that 12 also closely approximates a simple sine wave. It therefore follows that circuits of widths between 90 and 60 electrical degrees will have in them flux waves very close to the simple sine wave. Of course the curves 4), o, v, are equally representative for a greater number of poles, it being remembered, as before, that the arcs concerned are in every case electrical.

It will now be clear, if we have a motor with one lead per pole (as in F' 8) for the four pole connection, and means or changing it to a two pole connection as in Fig. 10, an if we chose a width of secondary circuit such that with the four ole connection it has that value previously escribed, between 180 degrees and 90 degrees which gives the best or most advantageous flux wave, that on cha ing to the two pole connection with two le s er pole this circuit will have a width lyvinnfi therefore have, for the latter connection, also a very close approximation to a simple sine flux wave.

12 and 13 explain the plan previously mentioned for avoiding serious sa'c cc of eflicienc in running at the lower speeds with few lea s per pole. Fig. 12 shows the ordinary way of constructing thesecondary of an induction motor, at the same time utilizing all the available copper space. The bars are all short-circuited to a common ring,..and phase or sixteen leads for four the electrical arc of each circuit is therefore eight leads for two poles. In F to distribution curve is obtain that some ending to the peripheral distance between a jacent bars or conductors. Fig. 13 shows 111 plan, alternatebars being connected, so t e electrical arc is twice that in Fig. 2, and the available copper space all ut1 ized. By connecting every third bar the arc will be three times that of Fig. 12, etc. Any desired width of arc may therefore be D obtained.

In Fig. 15 is illustrated a system for practicing my invention in chan the number of poles and securin a desired ux distrib tion. The motor there shown is a single phase machine, with connections for four and two poles, with one lead per pole in the former arran ement. Each secondary circuit (not shown is sup osed to embrace 180 electrical degrees in t e four ole connections, and therefore to have the ux curve for that arc shown in 9, it being assumed that this approximation to a simple sine wave is close enough for the. purpose of sta'rtin and running for a short time at half spee the number of poles were doubled these circuits would embrace only 90 electrical deees each. If therefore for the lesser numer of poles the current be fed in at two points er flpole, pro erly spaced, there will result t 1e ux distri ution shown in Fig. 10 and consequently the flux wave for a 90 degree arc in Fig. 11. From Fig. 9, and as has een previously explained, it is seen that between 180 de rees and 90 de rees there is some electrica chord which give a very close approximation to a simple sine wave. This chord might have been determined by trial or calculation, and taken as that for the four pole connection, and another spacin r between the two current leads per pole o the two pole connection determined such that the approximation for the two poles would also be ve close. For a polyphase motor the sets of eads for each pole would be repeatcd for each phase, or each base introduced into the motor by a set 0 leads with the common use of some or all of them for different phases.

It should be noted that as shown in several of the figures but with particular clearness in F' 3, 4 and 5, it is often ossible to improve t e flux distribution without increasing the number of leads but b merely changing the method of their emp oyment. A motor having a sharp flux distribution wave would, as will be clear by what has gone before, require one lead per pole per base or in the case of a two phase motor, our leads for two poles and eight leads for four oles; there being re uired a total of eight eads for a motor whic is to operate at either two oles or four oles at leasure. In Fi 3 a at top distn ution as been obtamed by employing two leads per pole per 'an alternatin current motor adapt .poles and 4 a flat for four 0 es by using no more leads than for a sharp ux distribution curve, namely 8, and in Fig. 5 the same is true for two poles. That is, by the connections of Figs. 4 and 5 we ma obtain from a motor of e' ht leads a two po 0 connection and a four po e connection with a flat top distribution curve in each case instead of having to use 16 leads asin Fig. 3. This arises from the fact that in Figs. 4 and 5 instead of using separate and distinct sets of leads for each phase we have made the sets for the two phases overlap and thus made each lead common to the two hases. This plan can be followed in obtaining flux distriution curves other than flat top ones in which there would be required more than the equivalent of two leads per pole per phase. It can also be a lied to more than-two phases. It shoul be borne in mind that the ,grinciplejnvolved inobtainin a desired flux tier each phase the same w istribution is g has a se arate and distinct set of leads to the motor or obtainin the distribution or whether part or all 0 the leads are common to two or more bases.

In certain o the claims the motor to which the invention is to be applied is defined as one capable of exert' torgse at speeds other than synchronous By t is meant a motor which, in contradistinction to a purely induction motor, which can never operate at synchronism, can operate at synchronous speed for any or for each of the different numbers of oles and at other speeds can exert torque e an induction motor.

As will be readily understood, the motors described in this application may be reversed in the ordinary way by reversing one or more phases as may be necessary in the case of the polyphase machine and by reversin the main or the auxiliary phase in the case 0 the single phase motorsupplied with an out of phase component 0 poweri.

What I claim is:

1. The method of increasing the s eed of to operate with di erent numbers of po and inherently capable of delivering for each number of poles the same torqlilie at two different speeds, and the s eed of t e load to which it may be connecte which consists in allowmg the motor to attain the desired torque at the higher speed corresponding to the torque, and changin the number of poles so that the motor, with the new number of poles, has an equal torque at the lower speed corresponding to the torque, as and for the purposes set forth.

2. The method of decreasing the s eed of an alternati current motor adapted to op erate with di erent numbers of poles and inherently capable of exerting for each number for one number of poles the volt of poles the same tor ue at two different speeds, and the eed 0 the load to which it may be connec which consists in allowing the motor to attam for one number of poles the desired torque at the lower speed corresponding to the torque, and changingl the number of poles so that the motor, wit the new number of dpoles, has an equal torque at the her s corresponding to the torque, as an for t e purposes set forth.

3. The method of varying the speed of a motor and that of the load to which it may be connected, between limits corresponding to different numbers of oles, which consists in makin the change m one number of poles to t e other on a portion of the motor and successively carry-big on such change on unt' the other portions all the motor has been changed, as set forth.

4. The method of varying the s eed of a motor and that of the load to Whic it may be connected, between limits corresponding to different numbers of oles, which consists.

in ma the change.- rom one number of poles to e other on a portion of the motor, and carrying on such ch e progesssively on successive portions until fil the motor has been changed, as set forth.

5. The method of varying the speed of a motor and that of the load to which it may be connected, between limits corresponding to different numbers of oles, which consists in making the change rem one number of poles to the other on a portion of the motor; allowing the motor to approximate the ultimate speed of which it' is capable after the change; and repeating such ste s on the remammg portion or portions of t e motor -un' :il sill the motor has been changed, as set ort 6. The method of increasing the s eed of an alternatfiflcurrent motor adapts to operate with erent s ds with difi'erent numbers of poles and inherently ca able of delivering for each number of poles t e same torque at two diflerent speeds, and the speed of the load to which it ma be connected, which consists in allowing 0 motor to attain for one number of poles the desired torque at higher speed correslpeonding to the torque and c anging the num r of poles and so that the motor, with the new number 0 poles and the new voltage, has an equal torque at the lower speed corresponding filo the torque as and for the purposes set ort 7. The method of decreasing the s eed of an alternat current motor adapte to operate with erent numbers of poles and inherently capable of exerting for each number of poles the same to us at two difierent speeds and the s 'eed o the load to which it may be connects which consists in allowing the motor to attam for one number of poles the desired torque at the lower speed corresponding to the torque, and changing the number of poles and the voltage so that the motor, with the new number of poles and the new voltage, has an equal torque at the high er speed corresponding to the torque, as and for the purposes set forth.

8. The method of brin current motor, capable o exerting torque at speeds other than synchronous, along with that of the load to which it may be connected, from a lower speed corresponding to a greater number of poles to a higher speed an alternating mates synchronism for the new num er of poles, as the speed increases, reducing the voltage to that normally desired; as and for the purposes set forth.

9. The method of bringing an alternating current motor capable of exerting torque at s eeds other than synchronous, along with that of the load to which it may be connected, from a lower speed corresponding to a greater number of oles to a higher speed corresponding "to a esser number of poles, which consists in reducing the number of poles, and increasing the voltage to a value in excess of that normally desired at or near synchronism for the new number of poles, so that at the instant the change has been completed and at the speed then existing the torque with the new number of poles and the new voltage will be sufficient to carry the load at increasing speed, then allowing the motor to increase in speed until it EPEZOXI- mates synchronism for the new num r of poles, and as the speed increases, reducing the voltage to that normally desired; agam reducing the number of polesand increasmg the voltage as described, allowing'the motor to attain approximately synchronous speed, andasthes edrisesreducingthevol to normal; an repea such ste unt' the desired ultimate s22? is reache as and for the pu oses set orth.

10. e method of bringing an alternating current motor, capable-of exerting torque at s eeds other than s chronous along with t t of the load to 'ch it may be connected from a her speed corresponding to a lesser num r of poles to a lower speed corresponding to a greater number of poles,

which consists in Increasing the number of poles, and dec I the voltage to a value m excess of that normally desired at or near synchronism for the-new number of poles,

completed and at the s so that at the instant the change has been completed and at the speed then existing the negative torque with the new number of poles and the new voltage will be suflicient to produce retardation, then allowing the motor to decrease in speed until it ap roximates synchronism for the new nuin er of poles, and as the motor decreases in speed, decreasing the voltage to that normally desired; asand for the urposes set forth.

11. The method 0 bringing an alternating current motor, capable of exerting torque at s eeds other than synchronous, along with t at of the load to which it may be connected, from a higher s eed corresponding to a lesser number of po es to a lower speed corresponding to a. greater number of poles, which consists in increasing the number of oles, and decreasing the voltage to a value in excess of that normally desired at or near synchronism for thenew number of poles, so that at the instant the change has been eed then existing the negative torque witi the new number of poles and the new voltage will be suflicient to produce retardation, then allowing the motor to decrease in speed until it approximates synchronism for the new number of poles, and as the motor decreases in speed, decreasing the voltage to that normally desired; again increasing the number of poles and decreasing the voltage as described, allowing the motor to attain a proximately synchronous speed, and as the speed decreases, decreasing the voltage to that normall desired; and repeating such steps until the esired ultimate speed is reached, as and for the urposes set forth.

12. he method of starting an alternatim current motor adapted to o erate with dii ferent numbers of poles, an inherently capable of delivering for each number of poles the same torque at two different speeds, and the load to which the motor may be connected, which consists in bringing it, by auxiliary means, to a speed ap roximating that of synchronism for one number of poles; and changing the number of poles so that the motor has with the new number of oles, the same or greater torque at the ower speed corresponding to that torque, as and for the urposes set forth.

. 13. he method of starting a single phase induction motor adapted to o erate with different numbers of poles, an inherently ea able of delivering for each number of po es the same torque at two different speeds, and the load to which it may be con nected, which consists in supplying to the motor a component of power displaced in phase from that of the main supply circuit, until the motor attains approximatelv svn- (-hronous speed for one number of poles; then disconnecting the source of displaced power component; and changing the number of poles so that the motor. with the new number of poles, has the same or greater torque at the lower speed corresponding to that torque, as and for the purposes set forth.

14. The method of starting a single phase induction motor, adapted to o erate with different numbers of poles, an inherently ca able of delivering for each number of po s the same torque at two different speeds, and the load to which it may nected, which consists in supplying to the motor a component of power displaced in phase from that of the. main supply circuit, until the motor attains approximately s nchronous speed for one number of po es; then disconnecting the source of the displaced power component; and reducing the number of poles and increasing the voltage so that the motor has the same or greater torque at the. lower speed corresponding to that torque with the new number of poles and the new voltage, as and for the purposes set forth.

15. The method of starting a single phase induction motor and the load to which it may be connected, which consists in supplying to the motor a component of power displaced in phase from that of the main supply circuit, until the motor attains approximatel synchronous speed for one number of po'es; then disconnecting the source of the displaced power component; reducii I the number of poles and increasing the ve tage to a value in excess of that normally desired at or near synchronism for the new number of poles, so that at the instant the change has been completed and at the speed then existing the torque with the new number of poles and the new voltage will be sufficient to carry the load at increasing speed, then allowing the motor to increase in speed until it approximates synchronism for the new number of poles, and as the speed increases, reducing the volta e to that normally desired; as and for t e purposes set forth.

16. The method of starting a single phase induction motor and the load to which it may be connected, which consists in supplying to the motor a component of power displaced in phase from that of the main supply circuit, until the motor attains approximately synchronous speed for one number of po es, then disconnecting the source of displaced power component; reducing the number of poles and increasing the voltage to a value in excess of that normally desired at or near s nchronism for the new number of poles, so

t at'the instant the change has been completed and at the speed then existing the torque with the new number of poles and the new voltage will be sufficient to carry the load at increasing speed, then allowing the motor to increase in speed until it approximates synchronism for the new number of poles, and as the speed increases,- reducing the voltage to that normally desired; again reducing the number of poles and increasing the voltage as to attain approximately chronous speed, and as the-speed rises, re ucin the v0 tage to normal; and repeati suc ste s until the desired ultimate sp is reache as and for the urposes set'forth. I

17. e method of varying the s d of an alternating current motor along with that of the load to which it may be connected and maintaining a 'ven approximatiom to a given flux distnbution, which consists in changing the number of poles by such step or steps that after each step has been comthe torque, positive or negative, will meted suflicient to cause change of speed toward with the next that co on to the new number of oles and feeding into the winding the numr oi currents per pole necessary to produce the app il-loximation desir 18. e method of varying the speed of an alternating current motor along with that of the load to which it may be connectedafid of obtaining for each po e number a desired approximation to a given flux distribution, w h consists in changing the number of poles by such step or ste s that after each step has been completed t e torque, positive or negative will be sufficient to cause cha e of speed toward that'corresponding to the new number of poles, and for each number of poles feeding'into the motor windi the current or number of currents per pi; e necessaryto roduce the approximation desired for that p0 e number.

19. The method of increasing the speed of an alternating current motor erting torque at other speeds than synchronous, along with that of the load to which it may be connected, and keeping the magnetic flux waves in the secondary circuits of the motors within any desired limit of departure from a given flux wave, which consists in decreasing the number of poles by such step or steps that after each step has been completed the torque willbe sufiicient to cause increase of until by such decrease of pole number t e limit of departure from the given flux wave has been approached, then increasing ste the number of currents per pole led into t e motor winding to such as Wlll bring the flux wave farther within the said limit of departure, then decreasing the pole number b the step or steps described until the sai 7 limit has again been ap proached, and continuing he T0069! "111511 the desired speed has been reac ed.

20. The method of decreasing the speed of an alternating current motor capable ofcxerting torque at other speeds than synchronous along with the load to which it may be connected and keeping, with the minidescribed, allowing the motor I capable of eirmum number of currents per pole fed into the motor windi the magnetic flux waves in the secondary circuits or the motor within any desired limit of departure from a given flux wave which consists in increasing the number of poles by such ste or steps that after each ste has been comp eted the negative torque Wlll be sufiicient to cause retardation until by such increase of pole number the flux waves in the seconds circuits are such that with the next step t e number of currents per pole may be reduced without exceeding the flux wave limit aforesaid, making this next etc and reducing the number of currents an continuing the steps in pole number described until the number of currents may ain be reduced, continuing this process until the speed desired has been attained.

21. The method of changin the speed of an alternating current motor ong with that of the load to which it may be connected from a speed corresponding to one number of poles to that correspond' to another numer of poles, and of maintaining in the motor any desired degree of appi'oximation to the best flux distribution which consists in changing the number of poles by such step or steps that after each step has been completed the torque, positive or negative, Wlll e sufiicient to cause achange in speed toward that corresponding to the ultimate number of poles, and changing with the last step the number of currents lper pole fed into the winding or windings of t e motor to that which will produce the desired degree of approximation to the best flux distribution.

22. The method of varying the speed of an alternating current motor along with that of the load to which it may be connected and of maintaining in the motor any desired de ee tion esired, which consists in changing the number of poles by, such a number that after the change has been com leted the torque, positive or negative, w' be sufficient to cause a change of speed toward that corresponding to the new number of poles, and changing with the change in the number of poles the number of currents per pole fed into the winding or of the motor to that which will produce the-desired degree of approximation to the desired flux distributron.

23. In an electric motor of which one element is adapted for variation in its pole numbers by variation in the number of points at which currents are led into its winding orwindings, and for variation in its flux distribution bv variation in the number of currents per ole fed into its win or windings, and 0 which the other element as electric circuits of such width or embracing an electric chord as will cause to be pro- 3 duced in them for one flux distribution and of approximation to the best flux distribu-v for one or more pole numbers, an a proximation to a desired flux wave whic shall fall within a given limit of departure from the desired flux wave, the method of var ing E the speed ofthe motor along with that o? the load to which it may be connected and maintaining the flux wave within the limit set, L which consists in varying the number of poles in the first element by such step or steps that the torque, ositive or negative, at the instant a step as been completed and at the speed then existing, will be sufficient to cause 3 c ange of speed toward synchronism for 1 each new number of poles; and when the departure from the given flux wave caused by 3 change in the number of poles approaches the predetermined limit, so that the next variation would cause the limit to be exceeded, changing with the next variation in the number of poles the flux distribution by chan ing the number of points er pole at whic the current or currents are ed into the first element to the minimum number necessary for the flux distribution which will maintain the flux wave within the predetermined limit as set forth.

RALPH D. MERSHON. Witnesses:

S. S. DUNHAM,

THos. J. BYRNES. 

